Light Emitting Diode (LED) based Fluorescent Microscopy versus Bright Field Microscopy for the Diagnosis of Tuberculosis from Extrapulmonary and Non-sputum Pulmonary Samples

摘要

Microscopy is the mainstay in the diagnosis of tuberculosis (TB) in resource poor settings. Usefulness of Auramine-O staining and LED (AO-LED) microscopy for the diagnosis of tuberculosis from extrapulmonary and non-sputum pulmonary samples was evaluated. A prospective study was performed on 75 extrapulmonary samples like CSF, Urine, Pleural fluid and non-sputum pulmonary samples like BAL. Smears were stained with auramine-O and Ziehl-Neelsen (ZN) stains and viewed under LED microscopy and bright field(BF) microscopy respectively. Solid culture (Lowenstein-Jensen medium) was used as a reference standard. Out of the 75 specimen collected, 24% of them were CSF followed by BAL specimen (23%) and pleural fluid (13%). Three (4%) were positive by AO-LED microscopy whereas only one (1%) was positive by ZN-BF microscopy. The percentage of TB positivity among the three different methods used, revealed a high yield by culture (8%), followed by AO-LED (4%) and ZN-BF (1.3%) methods. AO-LED microscopy had a better sensitivity of 50% Vs 16.6% in comparison to ZN-BF microscopy. Both AO-LED and ZN-BF microscopy methods had a specificity and positive predictive value of 100%. Both the techniques had a negative predictive value of 95.8% and 93.2% respectively. We found a higher smear positivity rate with AO-LED in comparison with ZN-BF microscopy. The AO-LED microscopy was found to be more sensitive than the ZN-BF (50% Vs 16.6%). We report that it would be prudent to use AO-LED microscopy for non-sputum samples like BAL replacing the current practice of ZN-BF microscopy for the diagnosis of smear negative pulmonary tuberculosis.